It may be a complex set of reasons. One is the long trigger pull of a double action compared to a single action semi like a 1911. The index finger is flexed by a muscle which can act with the other fingers holding the grip of the pistol. So that when the shooter contracts the index finger, he/she also to some extent flexes the other finger causing the pistol to move off target.

A shooter can overcome this tendency by repetitive training to address this issue. Placing an object (like a coin) on the barrel or slide of the gun, balance it there while maintaining the sight picture and dry firing the gun can help.

"When plunder becomes a way of life for a group of men living together in society,
they create for themselves in the course of time a legal system that authorizes it and a moral code that justifies it." Frederic Bastiat